Sounds like you're taking the long road to making a Mac mini, particularly since the opposite can also be done --- load the AppleTV interface onto a normal Mac ... however I recognize the component and HDMI outputs advantages of ATV. Good luck.

[Edit]: Keep in mind that talk of how-to-hack-an-ATV is out of scope here. This isn't an all-purpose AppleTV forum, but rather one for discussing HB projects for playing back on iPod/AppleTV.